Part 1 (1/2)

The Life of Crustacea

by William Thomas Calman

PREFACE

This sketch of the Natural History of the Crustacea deals chiefly with their habits and modes of life, and attempts to provide, for readers unfay, an account of soested by a study of the living animals in relation to their environment

I am indebted to the Trustees of the British Museuures prepared for the ”Guide to the Crustacea, Arachnida, Onychophora, and Myriopoda exhibited in the Departy”; also to Sir Ray Lankester, KCB, FRS, and to Messrs A

and C Black for the use of a nuures froy,” edited by Sir Ray Lankester

The source of these figures is indicated in the explanation attached to each Of the reraphs of specimens in the collection of the British Museum; the others have been drawn froures of various authors, by Miss Gertrude M Woodward, to whoiven to their preparation

W T C

CHAPTER I

INTRODUCTORY

Everyone has sorouped by naturalists under the name Crustacea The edible Crabs, Lobsters, Prawns, and Shriht to the table or as displayed in the fisher's, and the most unobservant of seaside visitorsspecimens of some of the more obtrusive species, such as the common Shore Crab Many, however, will be surprised to learn that the Barnacles coating the rocks on the seashore, the Sand-hoppers of the beach, and the Woodlice of our gardens, are members of the same class

Still less is it suspected, by those who have not given special attention to the subject, that the living species of the group nue diversities of structure and habits, and playing ieneral economy of Nature

In addition to those just mentioned, a few Crustacea are sufficiently well known to be distinguished by popular names, such, for example, as Crayfish and Hermit Crabs, but for the vast majority no nay In the following pages, therefore, while technical terly as possible, the unfamiliarity of the animals themselves makes it needful to use many unfadom, the Crustacea forroup, or Phyluroup have a more or less firments, there are jointed limbs, and some of these are modified to serve as jaws The chief divisions or classes of the Arthropoda are--(i) _Insecta_, including butterflies, Moths, Bees, Wasps, Flies, Beetles, and the like; (ii) _Chilopoda_, or Centipedes; (iii) _Diplopoda_, or Millipedes[1]; (iv) _Onychophora_, including the curious worm-like _Peripatus_; (v) _Arachnida_, or Scorpions, Spiders, Mites, and their allies; and (vi) _Crustacea_

[1] The Chilopoda and Diplopoda are sole class--Myriopoda

It is not easy to summarize in a feords the characters co theuide to classification, it is useful to re three pairs of walking legs, an Arachnid by having four pairs, and a Centipede or Millipede by having a great many pairs, all nearly alike The Crustacea, on the other hand, show great diversity in the nus, but they rarely show any special reseroups of Arthropoda Thus, for exaare_, is very siinata_, but it has only seven pairs of walking legs, while the Millipede has seventeen or nineteen pairs

More precisely, it reatby gills or by the general surface of the body, having two pairs of ”feelers,” or antennae, on the front part of the head, and at least three pairs of jaws Exceptions to each of these state with parasites and other highlystages afford indications of affinity, and comparison with less modified forms enables us to trace a connection with the typical Crustacea

The best way to forroup of animals, however, is not to attein by studying the structure of some typical and central species, and afterwards to note the divergences fro very generally, it ences are of two kinds On the one hand there are characters that have no apparent relation to the animal's habits and mode of life, and on the other hand there are modifications of structure which are more or less plainly of use to the animal It is to characters of the former class that we look for evidence of an animal's affinities, and it is upon them that our systems of classification are chiefly based The characters of the second class--”adaptive” characters, as they are called--beco concern,” so to speak, and endeavour to understand how its life is carried on in relation to its surroundings

In pursuance of this plan of study, the next chapter will be devoted to a description of the Common Lobster as a type of the Crustacea In the third chapter a survey of the classification of the group will be given; since, however, the characters on which the classification is based cannot be explained fully without entering into technical details which are beyond the scope of this work, this survey will be restricted to what is necessary for co chapters In the fourth chapter soes of Crustacea, and of the changes they undergo in the course of development

In the next five chapters the Crustacea are classified according to their habitats, and those living in the shalloaters, the depths, and the surface of the ocean, in the fresh waters, and on land, are discussed in turn; while a separate chapter is devoted to the curious forms that live as parasites on, or as associates with, other animals

The last two chapters deal respectively with the Crustacea as they affect roup as revealed by fossil remains